1. Field of the Invention
The present invention relates to an aqueous emulsion composition and an adherent composition and, more particularly, to an aqueous emulsion composition and an adherent composition suitably used as a primer or adhesive.
2. Description of the Prior Art
Organic solvent adhesives are generally in wide use as an adherent composition used for adhesive bonding of a variety of molded products such as plastic films, plastic sheets, plastic foams, fibers, synthetic leathers, and metals.
The organic solvent adhesives have high adhesion strength for relatively rigid molded products, so that they are used for a variety of applications, while on the other hand, they have disadvantages of being at risk of catching fire and being not so desirable in environmental sanitation. In view of these disadvantages, in recent years, aqueous adhesives have been increasingly developed as a substitute for the organic solvent adhesives.
Adherent compositions comprising aqueous emulsion containing ethylene-vinyl acetate copolymer are known as the aqueous adhesives. For example, European unexamined patent publication bulletin of EP1106628A1 proposes an aqueous emulsion composition comprising modified carboxyl resin of saponified ethylene-vinyl acetate copolymer and surface-active agent and describes that this aqueous emulsion composition, when used as an adherent composition, provides high adhesion strength for a wide variety of materials and provides adequate adhesion even for molded products.
To be more specific, EP1106628A1 describes that modified carboxyl resin of saponified ethylene-vinyl acetate copolymer is emulsified in water by using a surface-active agent, to prepare an aqueous emulsion composition, first, and, then, unsaturated ethylenic monomer and photo polymerization initiator are optionally mixed in that aqueous emulsion composition, whereby an adherent composition having high adhesion strength is produced.
It is true that the adherent composition described in EP1106628A1 affords adhesion at higher adhesion strength than the known adherent composition comprising aqueous emulsion containing ethylene-vinyl acetate copolymer. But, since this adherent composition is produced in such a manner that after modified carboxyl resin of saponified ethylene-vinyl acetate copolymer is emulsified by using a surface-active agent, unsaturated ethylenic monomer and photo polymerization initiator of high hydrophilic nature (in other words, high polarity) are optionally mixed in the aqueous emulsion composition thus prepared, the adherent composition is insufficient in wettability for the object to be adhesive bonded or the object to be adhesive bonded of low surface polarity, in particular, for the reason of which there is the possibility that the adhesive bonding properties may be insufficiently developed. Also, since the emulsion is not stable sufficiently, there is the possibility that poor mechanical stability and poor storage stability may be caused.